Conventionally, a technology of calculating an available mileage over which a vehicle can still travel without refilling (an available cruising range) based on a residual amount of fuel has been proposed for a gasoline vehicle which runs on gasoline as fuel (for example, refer to Patent Document 1). The calculated available cruising range is displayed on an instrument panel for the driver to uses it as an index of economical driving or in making a driving plan.
In the technology described Patent Document 1 above, firstly, the fuel consumed and the distance covered by the vehicle are each added up to calculate a fuel consumption rate (fuel economy) which is expressed in units such as miles or kilometers per unit volume of fuel, whereafter an available cruising range is calculated based on the fuel consumption rate and the residual amount of fuel.